Voltage regulator circuits are used in semiconductor devices to provide a stable DC (Direct Current) output voltage with little fluctuation to a load. Such regulators are also known as Low Drop Out (LDO) regulators. Typically, LDO regulators rely on feedback voltage to maintain a constant output voltage. That is, an error signal whose value is a function of the difference between the actual output voltage and a nominal value is amplified and used to control current flow through a pass device such as a power transistor, from the power supply to the load. The drop-out voltage is the value of the difference between the power supply voltage and the desired regulated voltage. The low drop out nature of the regulator makes it useful in portable devices such as cameras, which have a battery power supply.
Over-current protection is typically required when a short-circuit condition occurs in the output of a regulator circuit. Over-current protection can be achieved by monitoring the current delivered to a load and then clamping the current when it exceeds a predetermined maximum level. Such circuits may require a reference current that is greater than the bias current of the rest of the regulator, or have floating currents.
For small, battery-powered devices, it is important to conserve the charge in the battery. Thus, there is a need for a series regulator that does not require large reference currents or have floating current, and can be readily implemented on a semiconductor integrated circuit.